Internal combustion engines with increased fuel economy and decreased harmful emissions, for example as used in automotive vehicles, are the subject of much research and development. One area of research in internal combustion engines is focused on the valve train which is responsible for opening and closing air intake valves which allow air into combustion chambers of the internal combustion engine and which is also responsible for opening and closing exhaust valves which allow combustion products out of the combustion chambers. Throughout the remainder of this section, the intake valves and exhaust valves will be generically referred to as combustion valves. As is known in the art of internal combustion engines, one or more camshafts are used to open and close the combustion valves. The camshaft includes one or more lobes which are eccentric to the axis of rotation of the camshaft. A camshaft follower interfaces directly with a camshaft lobe and translates the rotating motion of the camshaft into opening and closing motion of the combustion valve in a cyclic manner during operation of the internal combustion engine.
In order to allow for flexibility under different torque requirement conditions during operation of the internal combustion engine, variable-lift camshaft followers have been developed which are switchable between a high-lift mode which opens the combustion valve by a first magnitude and a low-lift mode which opens the combustion valve by a second magnitude that is less than said first magnitude. In this way, the quantity of air allowed into the combustion chamber is varied depending on the operating conditions of the internal combustion engine. For example, when the internal combustion engine is operating in a low-torque condition, the low-lift mode can be selected in order to maximize fuel efficiency while achieving the torque demands of the internal combustion engine. Conversely, when the internal combustion engine is operating in a high-torque condition, the high-lift mode can be selected in order to maximize torque output of the internal combustion engine.
With the introduction of variable-lift camshaft followers to internal combustion engines, it is also necessary to diagnose the variable-lift camshaft followers in order to ensure that they are operating as desired. This is necessary to comply with OBD II diagnostic requirements as well as to avoid damage to other components of the internal combustion engine when a variable-lift camshaft follower is not operating as desired.
One existing diagnostic strategy for diagnosing variable-lift camshaft followers includes engine airflow-based algorithms. However, this approach may suffer from a signal to noise ratio issue that does not permit adequate diagnostic of the variable-lift camshaft followers at all times or over all operating conditions.
Another existing diagnostic approach for diagnosing variable-lift camshaft followers includes the addition of proximity sensors that directly measure the lift movement of each variable-lift camshaft follower. However, this approach requires additional hardware which results in additional cost and complexity. Furthermore, the associated hardware, wiring, and software associated with the proximity sensors must also be diagnosed for OBD II compliance.
U.S. Pat. No. 7,024,304 to Fukasawa et al. and United States Patent Application Publication No. US 2009/0048729 to Waters et al. describe strategies which utilize a spark knock sensor in the diagnostic approach for diagnosing the variable-lift camshaft followers. However, these diagnostic approaches use the spark knock sensor to indirectly diagnose the variable-lift camshaft followers. More specifically, Fukasawa et al. uses actual spark knock detected by the spark knock sensor to diagnose the variable-lift camshaft followers and Waters et al. uses the spark knock sensor to detect the closing of the combustion valves in order to diagnose the variable-lift camshaft followers.
What is needed is method for diagnosing a variable-lift camshaft follower which minimizes or eliminates one or more the shortcomings as set forth above.